This Is What Caused The Biggest Extinction In Earth's History

Extinction is a scary word and a scary topic — but it's one that
needs talking about.

Why? Because it seems to be happening now. Scientists believe
Earth is on the verge of its
sixth mass extinction, an event that could devastate
ecosystems all over the globe.

Habitat destruction and overexploitation are some of the major
reasons so many plants and
animals are disappearing around the world, and most
scientists agree that human-caused climate change is soon to be
the number one threat.

The topic has inspired fascination and dismay from scientists and
science communicators alike. Earlier this year, science writer
Elizabeth Kolbert published her book "The
Sixth Extinction: An Unnatural History," and the Smithsonian
Channel recently released a new documentary called "Mass
Extinction: Life at the Brink." Both works describe some of
Earth's previous mass extinctions and explore what they can teach
us about the impending one.

The Great Dying

Out of the previous five extinctions, the most famous is the
Permian extinction — the worst of them all. It happened about 250
million years ago, and scientists believe it
killed off about 90 percent of all life on Earth, earning it
the nickname "The Great Dying." Clues from the fossil record give
us information about what species went extinct and when, but how
the extinction happened in the first place has been a puzzling
question for scientists.

One of the biggest theories involves a series of volcanic
eruptions, which took place about 250 million years ago in
Siberia. According to Smithsonian's "Mass Extinction," these
eruptions spewed enough lava to bury the continental US under a
layer 1,000 feet deep. In fact, there's an area of about 2
million square kilometers in Siberia that's still covered by
volcanic rock today — scientists call it the "Siberian traps."

But it's not the lava that would have caused the extinction: The
eruptions would have also released massive amounts of
climate-changing carbon dioxide into the air — enough to cause
the kind of disturbance that might kill off nearly every lifeform
on Earth.

Carbon dioxide is a heat-trapping gas. With trillions of tons of
CO2 being released into the atmosphere during the eruptions, the
Earth would have grown warmer over time. Many land animals would
have been unable to adapt to the rising temperatures.

In addition, the ocean would have absorbed much of the excess
carbon dioxide in the air. When CO2 mixes with water, a chemical
reaction occurs that causes the sea to become more acidic. This
phenomenon, called ocean acidification,
can be devastating for certain kinds of marine animals, like
corals, because it prevents them from completing the chemical
processes that allow them to build their protective shells. Many
of these lifeforms would have gone extinct as a result.

What we don't know

There are still some mysteries to be solved. Research published
last March in the journal Proceedings of the National Academy
of Sciences suggests that the Permian extinction took place over
an extremely rapid timescale: only about 60,000 years, or "a
geological blink of an eye," according to
The New York Times. The Times article also reports that most
scientists believe the Siberian eruptions lasted 1–2 million
years, so nobody is quite sure yet why the extinction itself
happened so fast.

There are also other theories besides the Siberian eruptions,
although they tend to circle back to the idea of massive amounts
of greenhouse gases changing Earth's atmosphere. For instance,
some researchers believe that a
microbe called Methanosarcina belched tremendous quantities
of methane into the atmosphere, changing the climate and causing
many of the same issues the Siberian eruptions theory describes.

For now, it's impossible to know the truth for sure.

These are issues worth studying, though. With Earth at the cusp
of yet another mass extinction, scientists are eager to
understand the processes that led to such events in the past,
especially if they're linked to carbon dioxide in the atmosphere.
With human-caused climate change at the forefront of scientific
discussions these days, information on past carbon-related events
could give scientists insight into how we can deal with, or even
prevent, such catastrophes in the future.

It could also help us understand and deal with the impacts of
human-caused climate change that are coming.